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Additional BGP Configuration
Routes with lower administrative distances are favored.
Distribute List
Use the distribute-list command to add route filtering functionality by assigning inbound and outbound
IPv4 access control lists (ACLs) to a BGP neighbor. Only one inbound/outbound pair of ACLs can be
configured for a particular neighbor.
(config-bgp-neighbor)#distribute-list [in | out]
Specifies an IPv4 ACL name. This is a standard or extended IPv4 ACL against which the
contents of the incoming/outgoing routing updates are matched.
in Applies route filtering to inbound data.
out Applies route filtering to outbound data.
Refer to IP ACLs in AOS (ADTRAN’s Knowledge Base article 3087) for information on
how to create a standard or extended IPv4 ACL.
eBGP Multihop
Use the ebgp-multihop command to configure the maximum hop count for BGP messages to a neighbor.
(config-bgp-neighbor)#ebgp-multihop
Specifies the maximum hop count of BGP messages to a neighbor. Range is 1 to 254 hops.
This command allows an eBGP neighbor to be on a network that is not directly connected. The default
time to live (TTL) for BGP messages is 1 since eBGP peers are normally directly connected. However, in
certain applications, a non-BGP device, such as a firewall or router, might reside between eBGP peers. The
ebgp multihop command is required in this case to allow updates to have a TTL greater than 1 and to
allow received BGP updates to be added to the BGP table when the next-hop address is not directly
connected.
It is also good practice to create a static route to reach the eBGP neighbor when the neighbor is more than
one hop away, as well as creating a backup route pointing to null 0 interface with a higher administrative
distance. These routes prevent unnecessary BGP traffic from traversing the wrong connection and prevent
the BGP neighbor relationship from incorrectly attempting to establish itself on that connection. It is also
possible that sending invalid BGP traffic to some providers might result in the connection being
automatically disabled by the provider as a security measure.
Fast External Failover
Use the bgp fast-external-failover command to enable the fast external failover feature.
(config-bgp)#bgp fast-external-failover
When failover is enabled, if the link interface goes down between this router and a BGP neighbor, the BGP
session with the neighbor is immediately cleared. When failover is disabled and the link goes down, the
session is maintained until the BGP hold timer expires (refer to Hold Timer on page 18).
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